Botanical Applications of the Carbon Replica Technique 



275 



Fig. 5. Shadowed carbon replica of a scale of Mallonioiuis 

 leboiinii. 



Fig. 7. Direct unsiiadowed electron micrograph of a scale 

 of Syniiiii I'cliiniilata. Fig. 8. Shadowed carbon replica of a 

 scale of S. echinulani. 



is a significant point since the plage does not show 

 the iodine reaction. On the basis of this evidence, it 

 seems Hkely that this surface film is, in fact, the 

 amyloid layer detected by the iodine reaction. 



The electron microscopy of the scales of Malloinonas 

 and Syniira. — One of the most interesting botanical 

 applications of the carbon replica technique has 

 been the study of the scales of Mollonionas and 

 Syniira. These organisms are classed in the Algae 

 and lie on the borderline between plants and ani- 

 mals. They are unicellular and covered with a 

 flexible armour of silica scales which are much used 

 in the identification of species and exhibit elaborate 

 characteristic ornamentation. Mallomonas has fairly 

 large scales and frequently long bristles. 



Electron micrographs of replicas provide an en- 

 hanced three-dimensional effect, differentiate be- 

 tween the inner and outer surfaces of the scales, and 

 permit the examination of complete organisms. 



The replica technique used was a single-stage 

 method, the scales being covered with a film of 

 carbon and then dissolved away with hydrofluoric 

 acid. Figure 5 shows a replica of a scale of M. 

 leboimii. The array of scales on the surface of an 



Fig. 6. Shadowed carbon replica of part of a cell of Mallo- 

 monas ptiniilio. (By courtesy of the J. Roy. Microscop. Soc.) 



organism is shown by replicas of whole cells, as in 

 figure 6 which shows one end of a cell of M. piiniilio. 

 This is a new species with scales differing only 

 slightly from another closely allied species. The 

 difterence can only be seen in the electron micro- 

 scope. 



The scales of Synura are much smaller and more 

 delicate than those of Mallomonas, and the case for 

 using replicas is not quite so strong. However, it has 

 been found that a complete picture of the structure 

 of the scale can only be obtained both by examining 

 scales directly and using replicas. For example, in 

 figure 7, which shows a scale of S. echiniilata photo- 

 graphed directly, the structure at the base of the 

 spike is clearly shown. In the case of the replica 

 shown in figure 8, this structure is absent, indicating 

 that it is actually internal. This fact is not revealed 

 by shadowing the scale itself. The inner surface of 

 the scale of S. echiniilata is not illustrated here; it is, 

 in fact, the other side of the punctate region shown 

 in both micrographs. The holes do not extend over 

 the whole of the inner surface. 



It is hoped that the electron microscope will clear 

 up many of the difficulties encountered in identifying 

 the species of these two genera. This work is de- 

 scribed in greater detail elsewhere (2, 3). 



The author is grateful to Prof. T. Harris of the Botany 

 Department, University of Reading, for his help with the 

 work on pollen, to Mrs. K. Harris with whom the work 

 on Malloiuoiuis and Synura has been carried out, and 

 also to Dr. P. B. Hora of the same Department with 

 whom the work on fungus spores is being carried out. 

 Permission to publish was given by Dr. T. E. Allibone, 

 F. R. S., Director of the A.E.I. Research Laboratory. 



References 



1. Bradi KY, D. F., These Proceedings, p. 268. 



2. Harris, K. and Bradlfy, D. E., Discovery, 17, .^29 (1956). 



3. — /. Roy. Microscop. Soc. (1957, in press). 



4. MUHLFTHAITR. K., Plaiita 46. 1 (1955). 



